Difference between revisions of "EDT:Writing statements"
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call .) using "binding.myService"
returning to myCallBackFunction
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call .() returning to myCallBackFunction
Revision as of 18:45, 13 February 2012
EGL provides two kinds of statements:
- General statements such as if and while, for processing the data that is immediately available to your logic.
- Action statements such as add and call, for accessing external data sources or invoking external logic.
The case statement responds to conditions at run time by executing one set of statements rather than another:
- You can test a criterion value. The following example invokes
function test() x Int = 3; case (x) when (1) myFirstFunction(); when (2, 3, 4) mySecondFunction(); otherwise myDefaultFunction(); end end
- You can test a set of logical expressions. The following example displays only "x passes":
function test() x Int = 3; y Int = 5; z Int = 7; case when (x == 3) SysLib.writeStdOut("x passes"); when (y == 5) SysLib.writeStdOut("y passes"); when (z == 7) SysLib.writeStdOut("z passes"); otherwise SysLib.writeStdErr("You will not see this message."); end end end
As shown, no more than one clause ever executes. Control does not “fall through” from one clause to the next.
The continue statement returns control to the start of a block of code controlled by a for, forEach, or while statement. The statement lets you return to a labeled statement of one of those kinds, or to the nearest embedding statement of one of those kinds.
Here is an example:
inputList int =[2, 4, 6, 8, 10, 12, 14, 16]; for(i int from 1 to inputList.getSize() by 1) SysLib.writeStdOut(inputList[i]); if((i % 3) != 0) continue; end // if SysLIb.writeStdOut(" "); end
The code displays each integer on its own line, inserting a blank line after each group of three.
The exit statement exits from a function, program, service, or run unit; or from a block of code controlled by a case, for, forEach, if, or while statement.
The for statement runs a set of statements in a loop that repeats until a counter exceeds a specified value.
The example code shows three variations of a for statement that adds the same set of numbers.
program MyTestProgram function main() inputList int =[10, 4, 6, 8, 2]; numberInList int = inputList.getSize(); sum = 0; // the first for loop increments by 1. for(i int from 1 to numberInList) sum = inputList[i] + sum; end SysLib.writeStdOut("sum after the first for loop is " + sum); sum = 0; // the second for loop has the same effect but specifies the increment value. for(i int from 1 to numberInList by 1) sum = inputList[i] + sum; end SysLib.writeStdOut("sum after the second for loop is " + sum); sum = 0; // the third for loop starts at the opposite side of the list and decrements by 1 for(i int from numberInList to 1 decrement by 1) sum = inputList[i] + sum; end SysLib.writeStdOut("sum after the third for loop is " + sum); end end
In each case, the variable
i was local to the for statement. Here is an alternative:
i int; for(i from 1 to numberInList) sum = inputList[i] + sum; end
After that code ends, the value of
i is available and equals
numberInList + 1.
The if statement runs a set of statements if a logical expression resolves to true. The optional else keyword marks the start of an alternative set of statements that run only if the logical expression resolves to false.
The following code shows how to embed If statements in other If statements.
program MyTestProgram // A binary search finds a value in a sorted (preferably short) list. function binarySearch(list int, lowIndex int, highIndex int, value int) returns(int) while(true) middleIndex int = (lowIndex + highIndex) / 2; if(list[middleIndex] == value) return(middleIndex); else if(list[middleIndex] >= value) highIndex = middleIndex - 1; else if(list[middleIndex] < value) lowIndex = middleIndex + 1; end end end if(highIndex < lowIndex) return(-1); end end end function main() myNumbers int =[-6, -1, 2, 4, 7, 9 ]; valueOfInterest int = -1; lowestIndex int = 1; highestIndex int = myNumbers.getSize(); location int = binarySearch(myNumbers, lowestIndex, highestIndex, valueOfInterest); if (location == -1) SysLib.writeStdOut("Did not find " + valueOfInterest + "."); else SysLib.writeStdOut("The value of interest is " + valueOfInterest + ", at location " + location + "."); end end end
Except for the call statement, all are now used for accessing a relational database.
In EDT version .8:
call MyInterfaceType.theFunction) using "binding.myService" returning to myCallBackFunction onException myExceptionHandler;
In EDT version .7:
myServiceVariable MyInterfaceType call myServiceVariable.theFunction() returning to myCallBackFunction onException myExceptionHandler;
For further details, see Accessing a service